The bezel on a backlight refers to the unilluminated area around the edge of the backlight that is typically covered using black tape. There are many methods for reducing the bezel width in the prior art. Direct view backlights, where light emitting diodes (LEDs) are distributed behind the liquid crystal display (LCD) and shine directly through, have a very low bezel width in principle, but in general are too thick and expensive for a small area application. Such small area applications (of display sizes approximately 15 inches in diagonal or less) typically use lightguides with patterned extraction features and edge emitting LEDs to illuminate the LCD. This enables less LEDs to be required and very thin form factors. However, the area around the LED must be obscured as the high brightness and non-uniformity of this area would mean a display could not be positioned over this area. This area incorporates flat panel connector (FPC) electronics, the LED itself and the mixing area of the lightguide, where it is not possible to achieve uniformity by extraction feature control alone. This obscuration would be the limiting bezel width, meaning that a black area of at least 2-3 mm exists at the LED end of the lightguide.
Reducing this bezel area to create more usable display area for the device size has been a source of study. A cross section of the types of conventional configurations are summarized below:
JP 4552095 (Chiaki et al., issued Sep. 29, 2010) and U.S. Pat. No. 7,838,375 (Xu et al., issued Nov. 23, 2010) both position the LEDs at the corner of the lightguide where the natural spread of the LED light better fills the lightguide area.
JP2010056030 (Shin, published Mar. 11, 2010) angles the LEDs in such a way as to efficiently spread light into the lightguide.
U.S. Pat. No. 8,451,398 (Mizuuchi et al., issued May 28, 2013), U.S. Pat. No. 8,755,007 (Momose, issued Jun. 17, 2004) and JP2010056089 (Tong et al., published Mar. 11, 2010) describe reflecting structures on the far side of the lightguide that efficiently reflect light back in order to make better the uniformity near the LEDs.
U.S. Pat. No. 8,911,133 (Sato et al., issued Dec. 16, 2014) utilizes an air-guide with LEDs illuminating an airgap between highly reflecting areas, and an array of apertures are used to achieve uniformity. This system is relatively thick and proposed mainly for lighting applications.
US 20090015753 (Ye, published Jan. 15, 2009), U.S. Pat. No. 8,427,603 (Ishikawa et al., issued Apr. 23, 2013) and U.S. Pat. No. 6,935,764 (Choi et al., issued Aug. 30, 2005) describe structures on the area near the LEDs molded into the lightguide in order to better spread the light to reduce the mixing area.
US20050180165 (Sato et al., published Aug. 18, 2005) describes a secondary lightguide member that makes the LED illumination more uniform into the main lightguide.
A number of patents such as US20110090423 (Wheatley et al., published Apr. 21, 2011) and JP2010040246 (Osamu, published Feb. 18, 2010) attempt to thin the structure by adding lightguide elements to an LED array as used in a direct view backlight. This is to reduce the thickness of a direct view system in order to achieve a thinner unit.
Attempts to hide the LEDs on an edge based system include U.S. Pat. No. 6,951,401 (Van Hees et al., issued Oct. 4, 2005) and US20060255346 (Kunimochi, published Nov. 16, 2006) where the LEDs and lightguide are wrapped around beneath the main lightguide, and secondary lightguides are used underneath the main lightguide.
Patents such as CN202210196 (Li, published May 2, 2012), WO2012133160 (Kazunori, published Oct. 4, 2012) and JP2006244825 (Hiroshi, published Sep. 14, 2006) use patterned filters above the LEDs or a structured diffuser to reduce the non-uniformity.
EP1862730 (Singo et al., published Dec. 5, 2007) describes an alternate system whereby the LED is structured to fit into a specially made structure at the front end of the lightguide in order to maximize the spread of the light from the LED.
Patent US20130222737 (Mizutani, published Aug. 29, 2013) describes gradient index (GRIN) materials in structures in the lightguide near the LED in order to spread light more efficiently.
All of the above patents or patent publications either increase the thickness of the backlight or improve the spreading of the light between the LEDs so that sufficient light reaches the closest area of the active area mid-way between the LEDs to achieve efficient uniformity. This then defines the closest bezel position. However, none of these patents or patent publications deal with stray light, i.e., light that fails to couple from the LED to the lightguide for some reason, such as misalignment or a gap between the LED and the lightguide. This invention is intended to provide a solution to this problem.